Heredity and Genetics PRINCIPLES OF GENETICS A OVERVIEW

Heredity and Genetics

PRINCIPLES OF GENETICS A. OVERVIEW “Like produces like, but not *exactly* like” REVIEW: Sexual reproduction → variation due to chromosomes *HEREDITY: transmission of traits from parents to offspring *GENETICS: science of heredity

B. A History Lesson *Gregor Mendel: 1822 -1884 *monk in monastery @ Czechoslovakia *Vienna- studied science and math- became a teacher *2 yrs later- returned to monastery; plant experiments *1866 - published data from 8 years of experiments *1900 - finally genetics recognized as major development *Mendel’s Experiments: *Studied pea plants (b/c clearly express traits like flower color, seed shape, seed color, and plant height) *large sample sizes- help ensure actual ratios present in population

*crossed “different” plants → ex. Purple flowers x white flowers *offspring of parental cross = first filial generation (F 1) *offspring of 2 nd cross = 2 nd filial generation (F 2) *Mendel produced 929 offspring– 705 were purple (3: 1 ratio) *DOMINANT TRAIT: form of a trait that dominates another trait; (prevents expression of another trait) (ex. Purple flowers) *appears in F 1 generation *RECESSIVE TRAIT: hidden in F 1 generation

*MENDEL’S HYPOTHESIS: *Mendel’s experiments saw recessive trait disappear in F 1 generation but reappear in F 2 generation *ASSUMPTION: for each trait, there must be a pair of factors- 1 comes from egg; 1 from sperm * “Factors” = GENES: contain information for every trait *Represented by symbols or letters *Capitals = dominant *lowercase = recessive EX. W= purple, w= white

*ASSUMPTION: 2 genes segregate during gamete formation *offspring = ratio depending on genes present EX. WW x ww Ww Ww Ww parents Ww F 1 ww F 2 Ww x Ww WW Ww Ww RESULTS: 1 WW : 2 Ww: 1 ww 3 purple: 1 white (similar to 705: 929)

*EASIER TO SEE WITH PUNNETT SQUARES: *Chart used to determine possible combinations of genes among offspring Gametes of 1 parent W EX: Ww x Ww W w w WW Ww Ww ww

*TEST OF SEGREGATION: 3: 1 ratio 1 st MAKE YOUR PUNNETT SQUARE: time but what if Ww x ww? ? ? W w *****50% white: 50% purple!!! w Ww Ww w ww ww

GENETICS TERMINOLOGY *ALLELE: either of 2 alternative forms of gene for particular trait ex. W or w *GENOTYPE: combo. of alleles for certain trait ex. WW, Ww, or ww *PHENOTYPE: appearance of trait ex. “purple” or “white” *HOMOZYGOUS: 2 of same alleles for given trait ex. RR, rr (deals w/ seed shape) or WW or ww *HOMOZYGOUS DOMINANT: 2 dominant alleles (WW) *HOMOZYGOUS RECESSIVE: 2 recessive alleles (ww) *HETEROZYGOUS: 2 different alleles for a trait ex. Rr or Ww

*are used to help determine the possible genotypes of parents and offspring

*are used to analyze the chromosomes present in a person

TIME TO PRACTICE PUNNETT SQUARES!!